1. Field of the Invention
The present invention relates to a method of producing a ferrule with an optical fiber.
2. Description of the Related Art
Heretofore, optical connectors have been used as one means for optically connecting optical fibers. Generally, an optical connector is formed by a process in which the front part of a resin coating of a coated optical fiber is peeled, and then, the thus exposed bare optical fiber is inserted and fixed in an optical-fiber-insertion hole (see e.g., Japanese Unexamined Patent Application, First Publication No. 2000-147320).
FIGS. 5 and 6 are longitudinal cross sectional views illustrating examples of a conventional ferrule with an optical fiber 110.
Each of these ferrules with an optical fiber 110 is structured such that a bare optical fiber 101 which is exposed at a front end side of a coated optical fiber 103 is inserted in an optical-fiber-insertion hole 114 of a ferrule 111 and then fixed by providing adhesive therein. The coated optical fiber 103 is formed from the bare optical fiber 101 and a resin coating provided thereupon.
The ferrule 111 is structured such that a capillary 112 made of zirconia or the like is fixed to a front end side of a ferrule body 113 provided with a flange 113a. The capillary 112 is provided with a connection-end face 112a and an optical-fiber-insertion hole 114 which is in the connection-end face 112a and in which the bare optical fiber 101 is inserted and positioned in place. Further, the ferrule body 113 is formed with a coated-fiber-insertion hole 116 in which the coated optical fiber 103 is inserted and housed.
In the ferrule 111 of FIG. 5, the coated-fiber-insertion hole 116 is provided within the range of the ferule body 113, whereas in the ferrule of FIG. 6, the coated-fiber-insertion hole 116 is provided within a range from the ferrule body 113 to a rear end side of the capillary 112. The coated-fiber-insertion hole 116 is larger in diameter than the optical-fiber-insertion hole 114. A tapered hole 115 is provided between the optical-fiber-insertion hole 114 and the coated-fiber-insertion hole 116, which are caused to communicate thereby.
However, in the case in which a front end portion of the coated optical fiber 103 is inserted and fixed in the ferrule 111 as shown in FIGS. 5 and 6, because the difference in shrinkage ratio between the diameter of the coated-fiber-insertion hole 116 and the diameter of the optical-fiber-insertion hole 114 is substantial, then a considerable amount of adhesive Ad inevitably presents in the tapered hole 115. As a result, because of shrinkage of the adhesive occurring during a curing operation or due to changes in temperature and because of inclusion of bubbles in the adhesive, substantial stress acts on the part of the optical-fiber-insertion hole 114 in the vicinity of the tapered hole 115, thereby resulting in deterioration of characteristics of the optical fiber.
Further, the diameter of the coated optical fiber 103 is, for example, approximately 0.9 mm and thus it is difficult to improve positioning accuracy of the coated-fiber-insertion hole 116 with respect to an outer periphery of the coated optical fiber 103. Therefore, there is generally a certain level of clearance (e.g., approximately 0.1 mm or more, as a difference between inside and outside diameters) between the outer periphery of the coated optical fiber 103 and an inner surface of the coated-fiber-insertion hole 116. As shown in FIG. 8A, when the optical fiber is inserted in the ferrule, a center line of the coated optical fiber 103 is likely to deviate from a center line of the coated-fiber-insertion hole 116 such that the coated optical fiber bends or becomes imbalanced due to friction or the like between the resin coating 105 and the inner surface of the coated-fiber-insertion hole 116. Alternatively, as shown in FIG. 8B, a front end of the resin coating 105 is likely to abut against the tapered hole 115 in a slanted (biased) manner such that stress locally acts on the resin coating. There is the fear that further deterioration of characteristics of the optical fiber may result due to damaging bends of the bare optical fiber 101. Incidentally, in FIGS. 8A and 8B, the adhesive between the optical fiber and the inner surface of the hole is not illustrated.
As described above, when the end of the coating of the coated optical fiber abuts against the inner surface of the tapered hole, or conversely when a gap which is provided between the end of the coating and the inner surface of the tapered hole is filled with adhesive, there is the fear that external forces may be generated and applied unevenly to the bare optical fiber due to reactive forces from the inner surface of the tapered hole, shrinkage of the adhesive or the like. It is therefore difficult to produce or assemble a high-performance ferrule with an optical fiber.